Backside illumination image sensors are devices in which a microlens and photodiode may be formed at a backside of a wafer, which may maximize illumination efficiency in some applications. In some frontside illumination image sensors, maximization of illumination efficiency may help overcome limitations in maximizing resolution and sensitivity degradation caused by metal lines.
Example FIGS. 1A and 1B illustrate sectional views of a frontside illumination image sensor and a backside illumination image sensor, respectively, in accordance with the related art. In the frontside illumination image sensor illustrated in FIG. 1A, a microlens 100 may be formed at a frontside of a wafer. Accordingly, light 150 passing through the microlens 100 may not be efficiently transferred to a photodiode 102 due to a metal interconnection 104, due to the photodiode 102 being disposed under the metal interconnection 104.
In the backside illumination image sensor illustrated in FIG. 1B, a microlens 100 may be formed at a backside of a wafer. Accordingly, light 150 that passes through the microlens 100 may be directly received by a photodiode 102, which may enhance light illumination efficiency.
Example FIGS. 2A to 2F illustrate sectional views of a process of manufacturing a backside illumination image sensor using an SOI wafer, in accordance with the related art. As illustrated in FIG. 2A, a metal interconnection 206 for an image sensor may be formed on an epitaxial layer 204 by performing a CIS process using an SOI wafer. As illustrated in FIG. 2B, a support wafer 208 may be bonded to an upper end of a wafer in which a CMOS process has been performed for thinning the wafer, through a wafer bonding process. As illustrated in FIG. 2C, the bonded support wafer 208 may be fixed. A grinding and chemical mechanical polishing (CMP) process may be performed on a Si substrate 200 to remove the Si substrate 200, thereby exposing buried oxide (BOX) 202, as illustrated in FIG. 2D.
As illustrated in FIG. 2E, the BOX 202 may be removed through wet etching. The epitaxial layer 204 in which a photodiode will be formed may remain. As illustrated in FIG. 2F, a color filter 210, a microlens 212, and a support glass plate 214 may be sequentially formed over the epitaxial layer 204, thereby completing the backside illumination image sensor.
In a process of manufacturing a backside illumination image sensor, Si oxide may be used or required as the etch stop layer for performing a wafer thinning process (e.g. a process that leaves a portion of silicon substantially equal to the thickness of a photodiode on a wafer and removes the other portion of silicon. An oxide layer may be required to be disposed under silicon. An SOI (silicon on insulator) wafer in which a BOX may be disposed between Si layers may be used as a substrate. However, a SOI wafer may be relatively expensive and require a complicated manufacturing process compared to the bulk Si wafer.